System.Data.DataTable计算功能详解

System.Data.DataTable计算功能详解 收藏
 using  System;
 using  System.ComponentModel;
 using  System.Data;
 using  System.Windows.Forms;
 namespace  WindowsApplication1
  ... {
      public   partial   class  Form1 : Form
       ... {
        
          public  Form1()
           ... {
             InitializeComponent();
         }
 
       
 
          private   void  button1_Click( object  sender, EventArgs e)
           ... {
 
              // System.Data.DataTable计算功能详解，转载请保留以下信息
              // 测试环境      vs2005,c#
              // 作者:         jinjazz
              // 作者blog:      http://blog.youkuaiyun.com/jinjazz/
           
 
             System.Data.DataTable table  =   new  DataTable();
 
 
              // 计算常量，可以没有初始化列
              object  test  =  table.Compute( " 1+1 " ,  "" );
             Console.WriteLine(test);
              // test=2;
 
             test  =  table.Compute( " 1+1 " ,  " false " );
             Console.WriteLine(test);
              // test=2;常数计算和filter无关
 
             test  =  table.Compute( " abs(1) " ,  "" );
             Console.WriteLine(test);
              // test=null，不知道为这个什么没有抱错，而且返回null,其他的数学函数都会抱错
 
             test  =  table.Compute( " 2%2 " ,  "" );
             Console.WriteLine(test);
              // test=0;
              // 其他函数参考下面的计算列
 
 
 
              // 初始化datatale
             table.Columns.Add( " id " ,  typeof ( string ));
             table.Columns.Add( " value " ,  typeof ( int ));
              for  ( int  i  =   1 ; i  <=   10 ; i ++ )
               ... {
                 System.Data.DataRow dRow  =  table.NewRow();
                 dRow[ " id " ]  =   " id " + i.ToString();
                 dRow[ " value " ]  =  i;
                 table.Rows.Add(dRow);
             }
 
            
 
              // test = table.Compute("value+1", "true");
               /**/ /// /抛出异常，这里必须是聚合函数
 
 
 
              // *************************************支持的聚合函数********************** //
            
              // 求数量
             test  =  table.Compute( " count(id) " ,  " false " );
             Console.WriteLine(test);
              // test=0;
 
             test  =  table.Compute( " count(id) " ,  " true " );
             Console.WriteLine(test);
              // test=10;
 
 
 
              // 求和
             test  =  table.Compute( " sum(value) " ,  "" );
             Console.WriteLine(test);
              // test=55;
 
              // test = table.Compute("sum(id)","");
               /**/ /// /抛出异常，这里不能是string
 
            
              // 平均
             test  =  table.Compute( " avg(value) " ,  "" );
             Console.WriteLine(test);
              // test=5;
 
 
              // 最小
             test  =  table.Compute( " min(value) " ,  "" );
             Console.WriteLine(test);
              // test=1;
 
              // 最大
             test  =  table.Compute( " max(value) " ,  "" );
             Console.WriteLine(test);
              // test=10;
 
              // 统计标准偏差
             test  =  table.Compute( " StDev(value) " ,  "" );
             Console.WriteLine(test);
              // test=3.02765035409749
 
              // 统计方差
             test  =  table.Compute( " Var(value) " ,  "" );
             Console.WriteLine(test);
              // test=9.16666666666667
 
 
              // 复杂计算
             test  =  table.Compute( " max(value)/sum(value) " ,  "" );
             Console.WriteLine(test);
              // test=0.181818181818182
 
               /**/ /* ******************************************计算列************************ */
 
             System.Data.DataColumn column  =   new  DataColumn( " exp1 " , typeof ( float ));
             table.Columns.Add(column);
 
 
              // 简单计算
             column.Expression  =   " value*2 " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=2;
 
              // 字符串函数
             column.Expression  =   " len(id) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=3;
 
              // 字符串函数
             column.Expression  =   " len(' '+id+' ') " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=5;
 
              // 字符串函数
             column.Expression  =   " len(trim(' '+id+' ')) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=3;
 
              // 字符串函数
             column.Expression  =   " substring(id,3,len(id)-2) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=1;  // substring的起始字符位置为1不是0
 
              // 类型转换
             column.Expression  =   " convert(substring(id,3,len(id)-2),'System.Int32')*1.6 " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=1.6;
 
              // 相当于sqlserver的isnull
             column.Expression  =   " isnull(value,10) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=1;
 
              // 三元运算符,相当于sqlserver的case when
             column.Expression  =   " iif(value>5,1000,2000) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=2000;
 
              // like运算符
             column.Expression  =   " iif(id like '%1',1000,2000) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=1000;
 
              // in运算符
             column.Expression  =   " iif(id not in('id1'),1000,2000) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=2000;
 
              // 嵌套的三元运算
             column.Expression  =   " iif(value>5,1000,iif(id like '%1',4000,2000)) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=4000;
 
 
              // 客户端计算所占总数的百分比
             column.Expression  =   " value/sum(value) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=0.01818182
 
 
              // 客户端计算差值,比如nba常规赛的胜场差
             column.Expression  =   " max(value)-value " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=9
 
           
              // ***********************父子表计算*************************************/
 
 
              // 初始化子表,父子表关系
             DataTable tableChild  =   new  DataTable();
            
             tableChild.Columns.Add( " id " ,  typeof ( string ));
             tableChild.Columns.Add( " value " ,  typeof ( int ));
 
             System.Data.DataSet ds  =   new  DataSet();
             ds.Tables.Add(tableChild);
             ds.Tables.Add(table);
             DataRelation relation  =   new  DataRelation( " relation " , table.Columns[ " id " ], tableChild.Columns[ " id " ]);
             ds.Relations.Add(relation);
 
              for  ( int  i  =   1 ; i  <=   10 ; i ++ )
               ... {
                 System.Data.DataRow dRow  =  tableChild.NewRow();
                 dRow[ " id " ]  =   " id1 " ;
                 dRow[ " value " ]  =  i;
                 tableChild.Rows.Add(dRow);
             }
 
 
              // 计算子表记录数
             column.Expression  =   " count(child(relation).value) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=10;
            
 
 
              // 计算父子表的百分比
             column.Expression  =   " value/sum(child(relation).value) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=0.01818182;
 
 
              // 计算父子表的差值,比如父表为库存数量，子表为订购数量，计算得出需要补充的数量
             column.Expression  =   " iif(value-sum(child(relation).value)>0,0,value-sum(child(relation).value)) " ;
             test  =  table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
             Console.WriteLine(test);
              // test=-54;
 
              // 比较遗憾的是没有发现能够计算同比和环比的方法，而且计算列无法作为约束
              // ************结束，DataTable可以让你尽量发挥聪明才智来减少繁杂的sql语句并且减轻服务器计算符合^&^                         
         } 
     }
 }